<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>jq-first</title>
</head>
<body>
    <div class="main"></div>
    <div class="main"></div>
    <div class="main"></div>
    <script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.js"></script>
    <script>
        //在使用jQuery的时候 $表示jQuery,可以直接只用$替换对jQuery的书写
        console.log($('.main')[0])
        console.log(jQuery('.main')[0])
        //为标签设置样式
        $('.main').css({
            'background-color':'red',
            'width':'200px',
            'height':'200px'
        })
    </script>
</body>
</html>